Current electronic yarn changing devices for a circular knitting machine are as disclosed by the U.S. Pat. Nos. 4,137,732, 4,193,274, 4,385,507, 7,607,324, 7,836,731, 7,861,559 and 9,683,321, and the Japanese Patent Application No. 2005-042260.
With respect to the U.S. Pat. No. 7,861,559, the patent discloses a yarn feeding device for a circular knitting machine. The device includes a supporting element, which is arranged on the inner side of the machine bed and supports a set of yarn guides arranged side-by-side. Each of the yarn guides comprises a passage for at least one yarn to be fed to the needles of the machine arranged in the bed and the supporting element. Further, for each of the yarn guides, the supporting element supports an element for clamping and cutting the yarn dispensed by the corresponding yarn guide. A first member for actuating the yarn guides is provided to produce their passage from an inactive position, in which they are arranged so that their passage lies on the inner side of the knitting bed, to an active position, in which they are arranged so that their passage lies on the outer side of the needle bed, or vice versa, producing the passage of the yarn guides from the active position to the inactive position. A second member is provided for actuating the clamping and cutting elements and producing the passage for the clamping and cutting elements from a position for clamping the yarn to a position for waiting for the yarn to be clamped. The first actuating member is also configured on the supporting member and includes individual actuators. The individual actuators can be actuated to produce the passage of each of the yarn guides from the inactive position to the active position or vice versa, or vice versa, from the active position to the inactive position. Although having significantly reduced the using of a linking rod structure, the above patent includes a complex driving structure. More specifically, the patent utilizes two pneumatic tanks for performing the control of yarn feeding plates, and utilizes an additional independent pneumatic tank to control the mobile blade plate. Thus, due to the driving structure, the electronic yarn changing device of the above patent cannot provide a simplified overall structure.